In the field of surgery, and in particular ophthalmic surgery, it is desirable to provide a system which enables or facilitates the ability of a surgeon to perform a variety of surgical procedures upon an eye. Such procedures include vitrectomy, lens fragmentation, ultrasonic phaco emulsification, and irrigation/aspiration. Such procedures include excising internal tissues of an eye, and may, in certain cases, be followed by what is known as a "fluid-gas exchange". A fluid-gas exchange consists of the infusion of a gas into an eye to express the fluid from the eye to thereby control the intraocular pressure during and after the surgical procedure, as well as to facilitate further surgery within the eye while it is filled with gas.
Accordingly, there is a great need for a suction control system in which the negative pressure level can be very highly controlled. For cutting instruments, such as the vitrectomy probe, which draw tissue into the cutting port by the use of suction, the process of tissue removal is effectively controlled by the level of suction, which is directly related to a negative pressure level. Thus, controlling the negative pressure level to a fine degree is highly desirable to provide the surgeon a concomitant degree of control of the tissue excising process.
In addition, there is also a great need for a pneumatic power delivery system in which the dynamic pressure level applied to an instrument can be highly controlled. One such instrument is a pneumatic scissors handpiece, otherwise termed an intraocular microscissors. For example, when an ophthalmic surgeon is cutting periretinal membrane with a pair of intraocular scissors, one of the blades must be gradually inserted or "teased" under the membrane without damaging the underlying retinal tissue, and the other blade must be closed and opened gradually to prevent irreversible trauma to the retinal tissue.
In order to avoid any irreversible damage to a patient's eye the suction and pressure control system must be precisely responsive to the surgeon.times.s control inputs. There remains an intense need for a higher level of performance than has heretofore been achieved, particularly with regard to speed of response and stability of control.